The present invention relates to a process for the preparation of nitroaminobenzenes from aminobenzenes which are protected at the nitrogen, by nitration in the presence of inert, water-immiscible organic solvent and/or diluents.
It is known to prepare nitroacylaminobenzenes and the corresponding nitroaminobenzenes by employing a one-vessel process, starting from aminobenzenes, first reacting these with acylating agents, such as acetic anhydride, benzoyl chloride or p-toluenesulphonic acid chloride, in the presence of inert organic solvents, preferably in monochlorobenzene, at an elevated temperature, and then nitrating the products, without intermediate isolation, at 25.degree. to 50.degree. C. (compare U.S. Pat. No. 2,459,002, Examples 1 to 8).
Disadvantages of the process described in the U.S. patent specification are the low yields and poor qualities of nitroaminobenzenes, as is shown by repeating Examples 2 and 4 of the U.S. patent specification (since the examples of the U.S. patent specification themselves do not state the yield and product quality).
Since, in the process of U.S. Pat. No. 2,459,002, the acylation and nitration are carried out successively, that is to say without isolation of the acylated intermediate product, the nitration mixture always consists of excess acylating agent, liberated organic or inorganic acid, and nitric acid. This however has the disadvantage, in addition to the low yields and poor qualities of nitroaminobenzenes, that on subsequent neutralization of the reaction mixture more alkali is required than is actually needed for the neutralization of the nitric acid. As a result of the neutralization, the excess acylating agent and the organic or inorganic acid liberated are lost to subsequent economical utilization and furthermore the effluent is polluted by the salts formed during the neutralization.
A further disadvantage of the process described in the U.S. patent specification is that if the subsequent removal of the protective group is carried-out, without intermediate isolation of the nitroacylamino compounds, in an acid medium in the nitration mixture which has beforehand been neutralized and freed from chlorobenzene, large amounts of sulphuric acid are required (compare, in this context, U.S. Pat. No. 2,459,002, Examples 4 and 7, where, respectively, 6.6 and 4.4 mols of sulphuric acid are employed per mol of aminobenzene). Since, in this process, the removal of the protective group must furthermore be carried out in concentrated sulphuric acid, it is necessary that the sulphuric acid should, for isolation of the nitroaminobenzenes, first be diluted with water and then be neutralized with sodium carbonate. This produces large amounts of salt-containing effluents, which must be disposed of, or worked up, at considerable expense.
It has furthermore been observed, on repeating Examples 2 and 4 of U.S. Pat. No. 2,459,002 that, if 5-nitro-2-acetylaminoanisole or 3-nitro-4-acetylaminotoluene are cleaved in an acid medium, without intermediate isolation, some resinification occurs. To isolate the 5-nitro-2-aminoanisole or the 3-nitro-4-aminotoluene it is therefore necessary first to treat the reaction solution with active charcoal.
Further, it is known to prepare 3-nitro-4-aminoanisole by starting from 4-acetylaminoanisole, metering this, simultaneously with about 61.5% strength aqueous nitric acid, in the course of about 3 hours into an initial charge of monochlorobenzene, which already contains a part of the nitric acid required for the nitration, together with major amounts of sodium chloride, at 20.degree. to 30.degree. C. and cleaving the completely reacted nitration mixture with alkali, without intermediate isolation of the 3-nitro-4-acetylaminoanisole, after having neutralized the excess nitric acid and distilled the monochlorobenzene in steam (compare Bios Final Report No. 986, page 285-288).
An important disadvantage of this process is to be found in the fact that the nitration is carried out in the presence of large amounts of sodium chloride, whereby the effluent formed is additionally polluted. A further pollution of the effluent results from the sodium nitrate formed on neutralization of the excess nitric acid.
It is a further disadvantage that the chlorobenzene is removed from the nitration mixture, which has first been rendered slightly alkaline with sodium carbonate, by an energy-consuming steam distillation lasting about 5 hours, before the protective group is split off with alkali. Furthermore, the yields and qualities of 3-nitro-4-aminoanisole achieved are unsatisfactory.
It is known to prepare 3-nitro-4-aminotoluene by nitrating 4-acetylaminotoluene with the aid of an acid mixture containing nitric acid and sulphuric acid, in an inert solvent, such as methylene chloride (German Auslegeschrift (German Published Specification) No. 2,226,405).
However, this process has the disadvantage that in addition to the desired 3-nitro-4-acetylaminotoluene, 2-nitro-4-acetylaminotoluene is also formed as a byproduct, and this, after alkaline desacetylation, detracts from the quality of the 3-nitro-4-aminotoluene.
Furthermore, the yields of the desired reaction product, namely 88-91% of theory, are unsatisfactory for a commercial process.